Inhibition of lens epithelial cell migration at the intraocular lens optic edge: role of capsule bending and contact pressure

PURPOSE: To evaluate the inhibitory effect of a sharp intraocular lens (IOL) optic edge, a sharp capsule bend, and contact pressure between the optic edge and posterior capsule on lens epithelial cell (LEC) migration. SETTING: Department of Ophthalmology, Kyorin University, Tokyo, Japan. METHODS: This in vitro laboratory study evaluated a tumble-polished convex-plano IOL (CP group), an AcrySof IOL (Alcon) with a sharp edge (AS group), a new IOL with a round ridge (RR group), and a new IOL with a sharp ridge (SR group). The 2 new IOLs have high ridges and high angled loops that create firm contact between the ridge and posterior capsule. After sham cataract surgery, an IOL and a capsular tension ring (CTR) were implanted in the capsular bag of rabbit eyes. The extracted capsular bags containing the CTR and IOL were cultured. The inhibitory effect of each IOL on cell migration was analyzed. Furthermore, LEC migration on the posterior capsule was compared in culture between capsules having a sharp right angle and those with gradually curving bends. RESULTS: The inhibitory effect on cell migration was statistically greatest in the SR group followed by the RR, AS, and CP groups. A sharp capsule bend did not inhibit cell migration. CONCLUSIONS: The results suggest that inhibition of cell migration at the optic edge is regulated by the degree of contact pressure between the optic edge and posterior capsule. A sharp capsule bend might indicate strong contact but does not in itself inhibit cell migration.     

Adhesion of lens capsule to intraocular lenses of polymethylmethacrylate, silicone, and acrylic foldable materials: an experimental study

AIMS—To investigate the adhesion characteristics of several intraocular lenses (IOLs) to the simulated and rabbit lens capsule.
METHODS—Adhesive force to bovine collagen sheets was measured in water with polymethylmethacrylate (PMMA), three piece silicone, and acrylic foldable IOLs. In rabbit eyes, phacoemulsification and IOL implantation were performed. Three weeks later, adhesion between the anterior/posterior capsules and IOL optic was tested, and the capsule was examined histologically.
RESULTS—The mean adhesive force to the collagen sheet was 1697 (SD 286) mg for acrylic foldable, 583 (49) mg for PMMA, and 0 mg for silicone IOLs (p=0.0003, Kruskal-Wallis test). Scores (0-5) of adhesion between rabbit anterior capsule and IOL optic were 4.50 (0.55) for acrylic foldable, 3.20 (0.84) for PMMA, and 0.40 (0.55) for silicone IOLs (p=0.004). Scores between rabbit posterior capsule and IOL optic displayed a similar tendency; 4.50 (0.84) for acrylic foldable, 3.00 (1.00) for PMMA, and 0.40 (0.55) for silicone IOLs (p=0.021). Histological observation indicated that the edge of IOL optic suppressed the migration of lens epithelial cells towards the centre of the posterior capsule. This inhibitory effect was most pronounced with acrylic foldable IOL and least with silicone IOL.
CONCLUSIONS—The acrylic foldable IOL adhered to the lens capsule more than the PMMA IOL, and the silicone IOL showed no adhesiveness. These differences seem to play a role in preventing lens epithelial cells from migrating and forming posterior capsule opacification.

Keywords: intraocular lens; lens capsule; posterior capsule opacification; adhesion     

Mathematical modeling of the forces between an intraocular lens and the capsule

PURPOSE: To model the pressure relationship between an intraocular lens (IOL) and the capsular bag. SETTING: Department of Physics, Kings' College, London University, London, United Kingdom. METHODS: A mathematical model was made of the forces between the capsule and IOL showing that the pressure related to the local radius of curvature of the IOL at any given point. The local radius of curvature for round-edged and square-edged IOLs was measured from electron micrographs of the IOL profiles, and the corresponding pressure profiles were calculated and compared. RESULTS: The pressure between an IOL and the capsular bag was proportional to the quotient of the tension in the capsule divided by the local radius of curvature of the IOL, with a constant of proportionality that depended on the coefficient of friction between the capsule and IOL. Measuring the local radius of curvature of the 2 IOL types suggested a pressure increase of at least 69% +/- 6% at the optic edge with the square-edged IOL. CONCLUSIONS: The mathematical model predicted that IOLs with square-edged optic profiles exerts higher pressure on the posterior capsule than IOLs with round-edged optic profiles. The higher pressure may form a physical barrier to lens epithelial cell migration onto the posterior capsule.     

术后囊袋弯曲形成在屈光性白内障手术中的意义

屈光性白内障手术时代,术后后囊膜混浊（PCO）以及人工晶状体（IOL）位置异常已成为影响患者视觉质量的重要因素。笔者将从囊袋弯曲角度阐述白内障术后后发性白内障和IOL在囊袋内的稳定性。囊袋弯曲是术后囊袋和IOL锐利边缘贴合形成的屏障结构。完全黏附型囊袋弯曲不仅可以有效减少晶状体上皮细胞的迁移,而且提高IOL稳定性（包括轴向位移、偏心、倾斜及旋转等）。现立足于囊袋弯曲的形成演变过程以及不同分型,阐述了其预防PCO和维持IOL稳定性的机制,为提高白内障患者术后视觉质量提供思路及可行措施。     

Lens epithelial cell migration between posterior capsule and intraocular lens with variously finished posterior optic edge and two haptic angulations

PURPOSE: To compare lens epithelial cell migration between intraocular lens (IOL) optics and the posterior capsule of IOLs with various edges and haptic angulations. METHODS: Experimental acrylic IOLs with 3 types of finishing (none, polishing, tumbling and polishing) and 2 types of haptic angulation (10 and 15 degrees ) as well as 3 (AcrySof MA30BA, Sensar AR40, CeeOn 911) clinically implanted IOLs were inserted in rabbit eyes. Scanning electron-microscopic examination of IOLs was carried out before surgery and histological examination of lens capsules 3 weeks after surgery. The grading of lens epithelial cell migration under the IOL was made by scoring. RESULTS: Scanning electron-microscopic examination showed that the optic edge sharpness decreased according to the finishing in experimental IOLs. The AcrySof and CeeOn lenses had sharp edges and the Sensar had a rounded edge. The migration score was highest in the IOL with a rounded edge whereas it was lowest in IOLs with a sharp edge and large haptic angulation. There was no significant difference between the scores of clinically implanted IOLs. CONCLUSION: Sharpness of the optic edge may be a critical factor for the prevention of posterior capsule opacification and more important than haptic angulation in acrylic IOLs.     

Lens epithelial inhibition by PMMA optic: implications for lens design

It has been a clinical impression that posterior chamber lens implants in some way inhibit opacification of the posterior lens capsule after extracapsular cataract extraction. The mechanism of this inhibition is unclear; it may be related to mechanical contact or blockage of migration of lens epithelial cells, or possibly to the leeching of toxic factors from the lens itself. A better understanding of the exact mechanism of opacification inhibition may have important clinical implications for intraocular lens design. For example, some lens designs that facilitate Nd:YAG capsulotomy by physically separating the posterior chamber lens and the posterior capsule may result in less inhibition and in fact more opacification of posterior capsules. We performed in vitro tissue culture studies of the effect of the polymethylmethacrylate (PMMA) optic of a planoconvex intraocular lens on cultured rabbit lens epithelium. These studies demonstrated both inhibition of lens epithelial migration beneath the PMMA optic (plano side down) as well as metaplasia and necrosis of lens cells growing directly beneath the optic. The clinical implications of these studies for intraocular lens design are discussed.     

Preventing posterior capsule opacification by creating a discontinuous sharp bend in the capsule

PURPOSE: To clarify which factor--intraocular lens (IOL) design or material--contributes most to the inhibition of migrating lens epithelial cells (LECs). SETTING: Jinshikai Medical Foundation, Nishi Eye Hospital, Osaka, Japan. METHODS: After phacoemulsification, an acrylic IOL with sharp optic edges was implanted in 1 eye and a poly(methyl methacrylate) (PMMA) IOL with an optic design similar to that of the acrylic IOL in the contralateral eye of 4 rabbits. RESULTS: The Miyake view and histopathological findings 3 weeks after surgery revealed that the lens capsule wrapped tightly around the optic edges, conforming to a distinctly sharp rectangular bend there with both IOL types in all rabbits. The migrating-LECs were inhibited at the site, and a massive Soemmering's ring cataract was formed. CONCLUSIONS: The discontinuous sharp capsule bend created by the sharp optic edges in both IOL types appeared to induce contact inhibition of the migrating LECs. The preventive effect of an acrylic IOL on posterior capsule opacification may be design dependent.     

人工晶状体植入术后房水细胞因子的研究进展

白内障摘除联合人工晶状体植入术作为白内障最主要的治疗手段,人工晶状体的生物相容性一直是研究的热点。从宏观层面,人工晶状体的生物相容性主要反应在人工晶状体植入术后的并发症,如：眼内炎、角膜内皮水肿、虹膜后粘连、葡萄膜炎、后发性白内障等;人工晶状体的生物相容性微观主要表现在房水中的一些细胞反应,如：巨噬细胞、单核细胞、成纤维细胞及人晶状体上皮细胞等在人工晶状体表面的黏附、增殖,且术后并发症是由于房水中细胞因子连续作用于房水内细胞产生的,另一角度讲,房水中细胞因子是桥梁,它一定程度能反应人工晶状体的情况,能更全面的评价人工晶状体的生物相容性,有利于探究白内障术后并发症的发生的机制,提高人工晶状体的生物相容性。     

Effect of surface coating an acrylic intraocular lens with poly(2-methacryloyloxyethyl phosphorylcholine) polymer on lens epithelial cell line behavior

PURPOSE: To evaluate the effect of surface coating of an acrylic intraocular lens (IOL) with poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) on the behavior of the lens epithelial cell (LEC) line, alpha-TN4. SETTING: Department of Ophthalmology, Nihon University School of Medicine, Tokyo, Japan. METHODS: A hydrophobic soft acrylic IOL (AF-1, Hoya) was coated with MPC polymer. A noncoated IOL served as control. An IOL from each group was placed on the membrane of collagen I or IV of the cell culture dish. The alpha-TN4 cells were seeded in the insert. Cell behaviors (ie, cell proliferation and spreading) on IOLs and membranes were observed. Cell migration beneath the IOL optic portion was assayed using a computer software program (POCOman system) for posterior capsule opacification (PCO). Type I or IV collagen is the major matrix component of PCO or native lens capsule. RESULTS: Cell proliferation was more marked on the noncoated IOL than on the coated IOL. Type IV collagen accelerated proliferation more than type I collagen. Cell migration to the area beneath the IOL optic was more prominent in the group with the type I collagen membrane and noncoated IOL than in other groups. CONCLUSION: Coating an acrylic IOL surface with MPC polymer suppressed adhesion and proliferation of LECs, suggesting it improves IOL biocompatibility.     

Effect of round-edged acrylic intraocular lenses on preventing posterior capsule opacification

PURPOSE: To clarify the extent to which the adhesiveness of an acrylic material influences the formation of posterior capsule opacification (PCO). SETTING: Jinshikai Medical Foundation, Nishi Eye Hospital, Osaka, Japan. METHODS: Two types of AcrySof(R) intraocular lenses (IOLs) were prepared: round edged and tumbled. The AcrySof with round edges was implanted in 1 eye in a group of 4 rabbits and the tumbled IOL, in 1 eye in a group of 5 rabbits. In both groups, the contralateral eye received a conventional AcrySof with sharp optic edges. A histopathological examination was performed 3 weeks after surgery. RESULTS: With the round-edged AcrySof IOL, no capsular bend formed at the optic edge and abundant lens epithelial cells (LECs) migrated posteriorly. With the sharp-edged AcrySof lens, a sharp capsular bend formed and LEC migration was significantly inhibited. In eyes with a tumbled IOL, a capsular bend was created, but it was less marked than that created by the sharp-edged lens and there was slightly more LEC migration posteriorly. CONCLUSIONS: The AcrySof IOL lost its preventive effect on PCO when the optic was rounded. The effect of the AcrySof lens in preventing PCO is mainly a result of its rectangular, sharp-edged optic design. The acrylic material may play a complementary role by helping create a sharp capsular bend. Capsular bend formation is the key to the PCO preventive effect of an IOL.